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| United States Patent |
5,087,748
|
|
Finke
, et al.
|
February 11, 1992
|
Process for the continuous oligomerization of hexafluoropropene oxide
Abstract
A continuous process for the preparation of perfluorinated carbonyl
fluorides from hexafluoropropene oxide (HFPO), in which HFPO is
continuously oligomerized in a catalyst solution in devices which allow
separation of the heavy product phase from the catalyst phase during the
reaction, is described. Different oligomer distributions can be achieved
by choice of the catalyst and different operating temperatures. The
reaction itself takes place always in the substantial absence of the
product which is formed, and achieves a considerable saving in time.
| Inventors:
|
Finke; Manfred (Kelkheim, DE);
Siegemund; Gunter (Hofheim am Taunus, DE);
Strutz; Heinz (Frankfurt am Main, DE)
|
| Assignee:
|
Hoechst Aktiengesellschaft (Frankfurt am Main, DE)
|
| Appl. No.:
|
463391 |
| Filed:
|
January 11, 1990 |
Foreign Application Priority Data
| Current U.S. Class: |
562/851 |
| Intern'l Class: |
C07C 051/58 |
| Field of Search: |
562/851
|
References Cited
| Foreign Patent Documents |
| 203466 | Mar., 1986 | EP.
| |
Primary Examiner: Killos; Paul J.
Claims
We claim:
1. A process for the continuous preparation of perfluorinated carbonyl
fluorides of the formula
##STR3##
in which x denotes an integer from 1 to 31, comprising a catalyzed
oligomerization of hexafluoropropene oxide (HFPO), entailing a reaction
device which is composed of one or more reaction vessels and whose first
vessel is equipped with an introduction device which is attached on the
side in the lower third, with an appliance for controlling the level of
the contents, and with a drainage device located at the bottom, the
reaction device being charge with a catalyst solution allows structural
phase separation and catalyzes the oligomerization process of HFPO into
which HFPO is fed continuously at a temperature of -10.degree. C. to
+25.degree. C. through the introduction device and is thereby converted
into oligomers, entailing the mixture of catalyst solution and HFPO
oligomers which have formed being continuously separated into phases
underneath the introduction device, or after transfer into another
reaction vessel, and the heavier product phase being continuously removed
through the drainage device located at the bottom of the reaction system.
2. The process as claimed in claim 1, wherein the catalyst phase is
returned into the reaction vessel.
3. The process as claimed in claim 1, wherein the reaction is carried out
at temperatures from 5 to 15.degree. C.
4. The process as claimed in claim 1, wherein gaseous or liquid HFPO is fed
in.
5. The process as claimed in claim 1, wherein countercurrent reactors or
fluid-contact units are employed in the reaction device.
6. The process as claimed in claim 5, whereby bubble-cap or sieve-plate
reactors, packed columns, reactors resembling spray towers, or bubble
columns, loop reactors or jet tube reactors are employed.
7. The process as claimed in claim 1, wherein catalyst solution is
subsequently metered in continuously or discontinuously.
8. The process as claimed in claim 1, wherein a mixture of N,N,N',
N-tetramethylethylenediamine/acetonitrile, alone or with added CuCl, is
employed as catalyst solution.
Description
DESCRIPTION
The invention relates to a process for the continuous preparation of
oligomers of hexafluoropropene oxide (HFPO).
The catalyzed oligomerization of HFPO has been disclosed [Angew. Chem.
(1985) 97, 164]. It is carried out discontinuously in a stirred vessel or
stirred autoclave, with HFPO being passed in, while stirring, until a
particular level of the contents in the stirred vessel is reached. A
period without agitation is then necessary, where appropriate while
cooling the reaction mixture, in order to allow a phase separation of the
light catalyst phase and the heavy product phase. Precise phase separation
is, on the one hand, necessary in order that as little as possible of the
catalyst, which is often costly, is carried out with the product and, on
the other hand, the oligomeric acid fluorides should be contaminated as
little as possible with the catalyst mixture or parts thereof in order to
avoid possible problems in subsequent reactions or use of the HFPO
oligomers. The discontinuous procedure, which is the technique hitherto
practiced, is very elaborate and personnel-intensive and it leads, as a
consequence of the necessity for a period without agitation and the fact
that the reactor volume can often be utilized only inadequately, to small
space-time yields and, owing to the unavoidable non-stationary state over
long stretches, to variations in product quality.
The disadvantages can be eliminated by carrying out the oligomerization of
HFPO continuously in the types of fluid-contact apparatus which allow,
alone or in combination with additional apparatus, separation of the heavy
product phase from the catalyst phase during the reaction.
Accordingly, the invention relates to a continuous process for the
preparation of perfluorinated carbonyl fluorides of the formula
##STR1##
in which x denotes an integer from 1 to 31, preferably 1 to 8, and in
particular from 1 to 5, by catalyzed oligomerization of hexafluoropropene
oxide (HFPO), entailing a reaction device which is composed of one or more
reaction vessels and whose first vessel is equipped with an introduction
device which is attached on the side in the lower third, with an appliance
for controlling the level of the contents, and with a drainage device
located at the bottom, being charged with a catalyst solution into which
HFPO is fed continuously at a temperature of -10 to +25.degree. C. through
the introduction device and is thereby converted into oligomers, entailing
the mixture of catalyst solution and HFPO oligomers which have formed
being separated into phases underneath the introduction device, or after
transfer into another reaction vessel, and the catalyst phase optionally
being returned into the reaction vessel, and the heavier product being
removed through the drainage device located at the bottom of the reaction
system.
Reaction devices of this type, called fluid-contact apparatuses, are
described, for example, in Ullmanns Encyklopadie der technischen Chemie
[Encyclopedia of Industrial Chemistry], 4th edition, volume 3, pages 357
et seq., Verlag Chemie 1973.
Examples which can be employed are stirred reactors or stirred vessel
cascades, as long as these are connected to a separator and it is ensured,
by measures of reaction technology, that the mixture of catalyst phase and
product phase reaches the next reaction vessel or the separator. The two
phases are separated in the separator which is of adequate size; the
catalyst phase is returned, where appropriate, into the stirred vessel or
the cascade, and the product phase is transferred to a storage vessel. A
liquid-seal pump or a tubular reactor can be employed analogously.
Countercurrent reactors are preferred, such as, for example, bubble-cap or
sieve-plate reactors, packed columns or reactors resembling spray towers.
In these cases, the catalyst solution is fed in at the top, and the
countercurrent of HFPO is passed in at the bottom. The catalyst and
product phases run downwards and are collected underneath the HFPO inlet
and separated into the phases. The upper phase (catalyst phase) is drawn
off and returned to the reactor at the top. The heavy phase (product
phase) is drained into a storage vessel.
The reaction vessel is equipped with an appliance for controlling the level
of the contents, which ensures that the product phase which is located in
the lower part does not rise above the level of the introduction device.
It is ensured in this way that the HFPO is always introduced directly into
the catalyst phase.
A particularly preferred fluid-contact apparatus is a bubble column, loop
reactor or jet tube reactor, in which the gaseous or liquid HFPO is
advantageously passed into the catalyst solution above the phase boundary
between catalyst solution and product; the product which is formed sinks
downwards, owing to gravity, through the catalyst phase and is separated,
in a non-agitated zone below the metering-in point, into a separate phase
and continuously drained into a storage vessel. HFPO can be metered in as
gas or liquid.
HFPO oligomerization is an exothermal reaction. The heat which is produced
can be removed by a jacket cooler, incorporated heat exchanger or by an
external heat exchanger through which the catalyst solution is circulated
during the reaction.
Finally, in the case of the preparation of short-chain oligomers of the
formula (I) (x=1, 2, 3, 4), evaporative cooling is also possible by
continuously taking off the short-chain oligomers (especially when x=1) at
the top.
It is possible, where appropriate, for catalyst solution to be subsequently
metered, from a storage vessel, continuously or discontinuously, into the
actual reactor in order to replace catalyst which has been carried out
and/or to allow partial exchange of catalyst during the reaction.
It is possible to employ as catalysts known systems, for example silver
nitrate in polar organic solvents (DE-A 20 26 669), CuCl/CuCl.sub.2
/acrylonitrile/acetonitrile (DE-A 29 24 385),
KF/adiponitrile/acetonitrile, CsF/tetraethylene diglycol ethers, but
preferably N,N,N',N,-tetramethylethylenediamine/acetonitrile alone or with
added CuCl (see DE-A 39 01 000.7 of the same date, entitled "A process for
the oligomerization of hexafluoropropene oxide"), as long as the catalyst
has, advantageously, a high activity and a long useful life and allows
rapid and substantial phase separation. A high activity is desired in
order to ensure complete reaction of the HFPO which is fed in.
HFPO oligomerization results in different oligomer distributions depending,
in general, on the type of catalyst and operating temperature. These
criteria also apply to the discontinuous procedure. However, it should be
emphasized that the process according to the invention is suitable both
for the continuous oligomerization of HFPO to give acid fluorides of the
formula (I) with the emphasis on selectivity for (I) (x=2) and for the
continuous oligomerization to give higher acid fluorides
(I) (x=3 to 8).
The advantage of the fluid-contact apparatus employed according to the
invention for the oligomerization of HFPO is that a continuous procedure
is possible by allowing separation out of the oligomerization product, and
thus a low concentration of the product which is formed in the catalyst
phase, during the oligomerization. This ensures that the reaction always
takes place in the substantial absence of the product which is formed, and
this is associated with a considerable saving in time so that it is
possible to employ smaller and simpler reaction apparatus which has no
movable parts, for example stirring devices.
The procedure is simple and easy to carry out and thus less
personnel-intensive. Moreover, the quasi-stationary state during the
continuous oligomerization means that there are fewer variations in
product quality.
Higher HFPO oligomers, in particular the trimer, tetramer and pentamer of
HFPO, are used, for example, as building blocks for the preparation of
perfluorinated inert liquids. The dimer of HFPO is used, inter alia, as
intermediate for the preparation of perfluorinated propyl vinyl ether.
EXAMPLE
6 liters of a catalyst solution which is composed of 5.2 liters of dry
acetonitrile, 755 ml of dry N,N,N',N,-tetramethylethylenediamine and 20 ml
of water are introduced under protective gas into a bubble column
(stainless steel; jacket cooler; internal diameter of the bubble column
=11 cm). At 10 to 12.degree. C., 6 kg of HFPO per hour are introduced
through a sintered metal frit attached on the side of the column in the
lower third. The resulting HFPO oligomers collect in a non-agitated zone
below the metering-in frit. When the product phase has reached the device
controlling the level of the contents, which is located below the
metering-in frit, the HFPO oligomer phase is continuously drained through
a valve located at the lower end of the bubble-column reactor. After the
catalyst solution has reached the control mark it has an effective height
h.sub.eff of 62 cm (h.sub.eff =distance between gas-inlet frit and
catalyst surface during operation). The conversion is greater than 99%,
for example, after 158 kg of HFPO have been passed in, the following
oligomer distribution of the compound (I) is found (in % by mass):
______________________________________
##STR2##
S
% by mass
______________________________________
x = 1 15.00
x = 2 80.54
x = 3 4.46
______________________________________
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